The objective of the proposed research is to clarify the precision and validity with which the scalp recorded auditory response considered to reflect the activity of the eighth nerve and auditory brainstem structures can be interpreted. This objective will be approached through the development of acoustic signal generation and response acquisition and processing apparatus of which the properties are completely characterized and documented. This apparatus will be used for investigations on animals to determine the relationships between normal and experimentally induced abnormal function of the ear and variations in the 10 msec vertex-mastoid response auditory "brainstem response." Similar studies on normal hearing subjects, and on neurologically normal patients with documented peripheral hearing impairments, will be undertaken using the same apparatus and signal processing methods. Similar investigations will be conducted on animals with brainstem lesions and no damage to the ear, as well as on humans with clinical signs of brainstem lesions and documented hearing levels. These investigations should lead to better methods for distinguished abnormalities in the ear from those in the brainstem on the basis of variations in the 10 msec vertex-mastoid responses. These methods may be of particular clinical importance in cases, such as comatose patients, where other evidence relating to the peripheral auditory or central neurological source of abnormalities in the 10 msec vertex-mastoid responses is not available.